The invention relates to an intramedullary nail, preferably for the humerus, comprising a securing head for a hammering-in and aiming device, with the intramedullary nail having at least one transverse bore adjoining at the e securing head, and comprising an entry tip in the vicinity of which anchoring elements can be extended radially.
The intramedullary nailing per se is a gentle method for the operative treatment of fractures of long tubular bones. Important advantages consist in a very small access without scarring worthy of mention and in a closed setting of the fracture. In order to obtain a stable and rotationally secure intra-medullary fracture splinting, intramedullary nails are locked in the bone at both ends by means of pins or screws.
In the treatment of upper arm fractures this locking at the introduction location (near the insertion) is carried out with the help of an aiming bow which is secured at the end of the nail and which at the same time serves as a hand grip for the better introducibility of the intramedullary nail. In it, guides for the borer are provided, which can thus exactly encounter the holes from the outside which are present in the implant. Due to their small diameters a problem exists in almost all humerus intramedullary nails in a locking at the end which is remote from the insertion. Since a finding of remote implant holes with a long aiming device is very complicated and since the nail bends and twists over the length of the entire humerus, the insertion-remote locking takes place freehand under X-ray amplifier translumination. In this an existing hole which is about 4 mm in size must be sought in the implant from the outside and encountered with the borer, which is accompanied by radiation exposure and a high consumption of time.
Intramedullary nails with radially extendable anchoring elements in the vicinity of the entry tip are shown in U.S. Pat. No. 5,810,820. Radially emerging wire tips bore into the bone matter and provide a hold in the axial direction. The wires, which are provided with tips, have a cylindrical shape and are in each case seated in guides in the drawn-in state. The principle of the radial emergence is based on the wires being pressed through axial forwarding into a radial deflection in such a manner that they deform plastically. Through axial restoring the wires are again plastically formed back into a cylindrical shape. This arrangement has the disadvantage that the wire must in each case be plastically deformed for the change of direction. A function check prior to the insertion of the intramedullary nail includes the risk that the wires harden and become brittle through the plastic deformation. An omission of the function check is also not very sensible. Furthermore, the wires must be very precisely guided on all sides within the intramedullary nail in order that no bending takes place.
In an intramedullary nail for the humerus there is the further difficulty that the diameter of the intramedullary chamber is dimensioned to be very small and admits only intramedullary nails with small diameters. Individual guides which completely surround the wire can be manufactured only with a great cost and complexity.
It is therefore an object of the invention to provide a simply designed intramedullary nail.
This object is satisfied in that the anchoring elements of the nail are combined in a claw of curved wires, with the wires being elastically deformed inside the intramedullary nail in a not outwardly moved state and springing out radially when the claw is axially forwarded so that the anchoring elements can assume their original curved shape.
This arrangement has the advantage that the work for the radial penetration into bone material is already stored with the drawing back of the claw into the shaft of the intramedullary nail. A function check is possible at any time, since the wires are deformed only in the elastic region.
For the individual wire an open, cylindrical guiding groove which guides the wire tip and which is interrupted by a radial aperture is sufficient. For small shaft dimensions the guiding grooves can also be produced by slotting when the tip of the intraniedullary nail can be placed on later. The radial apertures taper in the direction towards the entry tip of the intramedullary nail and center the wires. At the same time a lateral support takes place at the radially emerging wires. A rotational securing already arises at the wire tips through the guiding grooves. In addition cams can be attached to the foot of the claw which run into the guiding grooves as an additional rotational securing. A setting screw is rotatably journalled in the foot of the claw which is however fixed to the claw in the axial direction. Through the combination of the wires in a claw the position of the pre-bent wires relative to one another can be predetermined. Instead of having the planes in which the wires are bent off pass concentrically through the longitudinal axis, more space for the elastic deformation of the wires is won when these planes have a spacing from the longitudinal axis. Transverse bores which lie in the vicinity of the securing head can be applied with an aiming bow in spite of the small diameters for a humerus intramedullary nail since its arm length is dimensioned to be very short. If the setting screw can be introduced from the side of the tip of the intramedullary nail, the hollow intramedullary nail can have a curvature in the region between the setting screw and the securing head. In such a case a flexible screwing tool is required in order to adjust the setting screw. The present intramedullary nail is not restricted to the humerus and can in principle also be used in other tubular bones.
A further improvement, which can be used quite generally for intramedullary nails, consists in designing an intramedullary nail to be elastic in bending in at least one predetermined zone of its shaft in order that it can follow a curvature of the intramedullary nail. In this it is obvious that this zone which is elastic in bending should not lie in the vicinity of a fracture location of a tubular bone. Particular advantages result when this zone which is elastic in bending can also be used as a tension spring, because it is for example formed as a singly or multiply threaded helix, of which the windings have a small predetermined spacing in the tensionless state in such a manner that in a complete compression of this helical spring its windings are only elastically deformed in order to facilitate the hammering in of the intramedullary nail. After the anchoring of a first end of the intramedullary nail a drawing force can be exerted from the opposite end of the intramedullary nail which tensions this helical spring in the drawing direction and then, while maintaining the drawing force at this opposite end of the intramedullary nail, a further anchoring can be applied. The helical spring as a tension spring then exerts a compression on the bone or on an intermediately lying fracture location respectively via the double-ended anchoring of the intramedullary nail, with it not being possible for the compression to diminish so rapidly due to the much weaker spring action of the tension spring in comparison with the rigid intramedullary nail, since a slight change of the spring excursion causes only a slight change of the compression force. The provision of such a zone which is elastic in bending is advantageous in particular everywhere that the anchoring of the two ends of an intramedullary nail can take place independently of the position of these two ends with respect to one another. In a hollow intramedullary nail, such as is shown in the following exemplary embodiments, the anchoring of the two ends of the hollow intramedullary nail is carried out independently of one another from the end of the securing head. The bending and tension spring is therefore cut out of the hollow shaft as a helix in order to allow room on the inner side for a flexible screwdriver. A construction of a complete intramedullary nail with a bending and/or tension spring in a predetermined zone is likewise useful when the anchoring of the two ends takes place independently of their position relative to one another. In patent application WO 98/02104 a complete intramedullary nail which is prolonged by a boring piece is shown, at the two ends of which an aiming device can be placed on independently of one another in order to anchor the respective end. Here as well a zone which is elastic in bending and possibly also elastic in tension and which lies in the central part between the transverse bores has no influence on the approaching of the transverse bores. If such a zone which is elastic in bending and possibly also elastic in tension is planned, bending deflections of more than 2xc2x0 are useful. In rigid curved intramedullary nails, bending zones with a bending deflection of 4xc2x0 to 9xc2x0 are usual. Intramedullary nails which are elastic in bending should also be deflectable in this range. What such a zone which is elastic in bending can look like is described in EP-B-0 614 020 for a flexible screwing tool and can be transferred to an intramedullary nail when the outer diameter of the zone which is elastic in bending is not greater than the outer diameter of the rigid part. In principle all forms of tension springs which are elastic in bending are possible, as long as they do not project beyond the shaft diameter.
In the following the invention will be explained with reference to exemplary embodiments.